Method of making acoustic diaphragms



Aug. 5, 1952 F. B. LENZ 2,605,855

METHOD OF MAKING ACOUSTIC DIAPHRAGMS I Filed Dec. 22, 1948 2 SHEETS--SHEET 1 II M 1| IN V EN TOR.

Aug. 5, 1952 F. B. LENZ METHOD OF MAKING ACOUSTIC DIAPHRACMS 2 SHEETSSHEET 2 Filed Dec.

Patented Aug. 5, 1952 METHOD OF MAKING ACOUSTIC DIAPHRAGMS Frank B. Lenz, St. Charles, 111., assignor to Hawley Products Company, St. Charles, 111., a corporation of Delaware Application December 22, 1948, Serial No. 66,628

6 Claims.

This invention relates in general to acoustic diaphragms and more particularly to an improved process for forming the corrugations which provide increased flexure between the border and the vibratile in an acoustic diaphragm.

,It has long been recognized in the acoustic diaphragm art that it is desirable to employ some method for increasing the flexibility of the dia phragm near the point where the diaphragm is secured to the loud speaker assembly. Manufacturers of acoustic diaphragms have solved the problem to a certain extent by making the portion between the border and the vibratile areas thinner and more flexible. In United States Patent 1,872,583, issued to Jesse B. Hawley, August 16, 1932, a preferred method is described for the making of diaphragms with a border portion for retention by a support or holding means and a thinner portion between the border portion and the body or cone part of the diaphragm whereby the freedom of vibration of the diaphragm is greatly enhanced. In the above mentioned patent. there is disclosed a method for making the thinner portion in the form of a corrugation between .the, border and the vibratile portions of the diaphragm. The advantages of such a thin corrugated portion are well known in the acoustic diaphragm art. Freedom of vibration of the vibratile portion is greatly enhanced because the thinner corrugated portion is easily flexed and reduces th tendency for the rigidity of the supporting portion to be transmitted to the vibratile portion.

An object of this invention is to provide a sound producing or reproducing diaphragm in which all sounds of the audible range will be faithfully reproduced.

Another object of this invention is to provide a sound producing or reproducing diaphragm which will have a low natural resonance.

A further object of this invention is to provide a sound producing or reproducing diaphragm which will permit maximum freedom or vibration of the vibratile portion without interference from the rigidly secured supporting portion.

A still further object is to provide a sound producing or reproducing diaphragm which may be molded in one simple design and then may be phragms called the natural resonance of the diaphragm. Diaphragms which vibrate to produce an induced resonant period also are subject to a natural resonance which is inherent with the diaphragm. This natural resonance interferes with the faithful transmission of the induced vibrations and causes distortion of the reproduced sounds.

By the practice of the present invention it is now possible to prepare acoustic diaphragms in which the carcass may be of greater bulk and lighter weight, and which will have a lower natural resonance than is possible in previously known diaphragms. This lowered natural resonance results in less interference with the reproduced sound waves emitted from the diaphragm and more faithful reproduction of the original sounds. None of the desirable flexibility is sacrificed, however, because a new method for molding the corrugations is employed which allows a lower natural resonance, but which retains the same flexible characteristics known in diaphragms made by previous methods.

The overall effect of greater bulk and lighter weight combined with a lower natural resonance in a diaphragm is made possible through the employment of this novel method of producing the corrugation in the diaphragm. According to the new method, the corrugation or corrugations are introduced between the border and the vibratile portion of the diaphragm by a subsequent processing over a previously molded and treated diaphragm corrugation. In general, the process involves molding a diaphragm directly out of a bath containing suspended fibers according to well known methods, except that the diaphragm may be of somewhat greater bulk and lighter weight than the usual diaphragm. Th premolded diaphragm is formed with a corrugation between the border and the vibratile portion and is placed in a humidifying atmosphere until it picks up a certain amount of moisture. Then the dampened diaphragm is subjected to a pressure molding operation in which the previously formed corrugation is reformed between embossing dies. The fibers at the point of corrugation are subjected to a distortion under pressure, and this disturbing of the fibers has a marked lowering efiect upon the natural resonance of the diaphragm.

The above objects, advantages, and capabilities will become more apparent from the following description of the drawings in which:

Fig. 1 represents a cross-sectional view of the male former with a molded carcass deposited thereon;

Fig. 2 is a cross-sectional view of a humidifying chamber employed for adjusting the moisture content of a pre-molded carcass;

Fig. 3 is a cross-sectional view of the restrike mold dies showing the cavity embossing die and the punch embossing di in position, and a dampened diaphragm between the dies; and

Fig. 4 is a crosssectional view of a finished diaphragm after restrike between the dies of Fig. 3.

Considering the drawings now in more detail, Fig. 1 shows the conventional type of former consisting of a heavy supporting form 1 arranged so that suction can be applied to the holes 2 in the form. Mounted over the form I is a perforated metal sheet or screen 3 which is designed to receive the deposited film 4 of accreted fibers. In practice suction is applied to the underside of the form I and the suction is transmitted through the holes 2 to the perforated screen 3. The suction applied to the underside of the screen causes a film or layer of fibers to be deposited on the screen when the former is immersed in a bath containing dispersed fibers. The area represented generally at 5 in Fig. l is the corrugation which is to be reformed by a subsequent operation. The formed diaphragm may be pressed and dried in any of the known ways if so desired, or it may be removed from the former in the damp state and reformed immediately.

Fig. 2 represents one type of humidifying chamber which may be employed in the practice of this invention for dampening dried diaphragms or for bringing the moisture content of diaphragms to a desired level. The preformed dia phragm 4 with the corrugation 5 is placed inside the chamber or case 6 upon a perforated support 7. The case is closed and the liquid 8 is agitated as by air under pressure which is admitted through the line 9 to the sparger Ill. The air in the case and surrounding the roughly formed carcass 4 becomes saturated with moisture and causes the carcass to absorb moisture until a desired dampness is achieved.

The dampened carcass 4 then is removed from the humidifier 6 and is placed on a male die H as shown in Fig. 3 for reforming and embossing the carcass. At this point it is also possible to employ diaphragms molded as in Fig. 1 and which have not been dried. The male die II is known as the punch embossing die because it contains the raised portions I2 and 13-. The female die M, which is called the cavity embossing die because of the depressions which correspond to the raised portions 12 and iii of the punch die, is lowered onto the damp carcass 4. Pressure is applied to the embossing dies I! and 14 causing the damp carcass to assume the shape of the dies. At this point the previously formed corrugation 5 in the carcass 4 is forced into the desired undulated wave corrugations which may be seen clearly at in Fig. 4. The fibers in the corrugated area are compacted and distorted shape to give the unusual results described herein.

It will be noted from Figs. 3 and 4 that other embossed designs may be incorporated into the body of the diaphragm. For example, the vibratile portion ie of the diaphragm may be embossed with the corrugations ii. The employment of the herein described restrikemethod of molding acoustic diaphragms is advantageous from an operational standpoint since it is possible to make the preformed roughly molded carcass in large numbers in standardized equipment. Then the operator may reform the preformed carcasses into any number of special designs as desired.

It should be understood that the present invention may be employed on diaphragms molded and treated by methods employed in the manufacture of acoustic diaphragms. The formed diaphragm may be dried and lacquer treated before dampening and reforming. In another method a resin or size may be incorporated into the beater with the slurry of fibrous materials so that the diaphragm formed requires no coating treatment. Such a diaphragm may be dried and stored for later reforming or it may be reformed While still in the damp state. In either case, it is preferred to reform a diaphrgam which has been resin or lacquer treated.

Compacting and distorting the accreted fibers at the corrugated area of an acoustic diaphragm made according to the above described process results in changing the resonance characteristics of the diaphragm to a marked extent. While a diaphragm made according to the previously known methods will seriously distort the reproduced sounds because of its natural period of resonance, a diaphragm made according to the present method is unusually free from such distorting tendencies. In other words, the natural period of resonance of the present diaphragm in which the fibers at the corrugated area are compacted and altered is such that distortion is minimized and sound is faithfully reproduced.

It will be seen from the foregoing explanations that the present invention provides a method for preparing molded fibrous acoustic diaphragms in a simple manner and subsequently reforming the diaphragm to achieve a heretofore unknown result. By the practice of this invention it is possible to achieve the flexibility which'is necessary for free vibration in a diaphragm, and at the same time to compact and disturb thefibersso as to change the natural. period of resonance of the diaphragm. The result is a diaphragm which faithfully reproduces sound without distortion from the natural resonance of the diaphragm.

The invention is hereby claimed as follows:

1. The method ofv making an acoustic diaphragm which comprises forming a seamless accretedfibrous diaphragm normally subject to undesirable natural resonance characteristics and having a border portion, a vibratile portion and a corrugation between said border and said vibratile portions, and reforming by pressing said accreted corrugation to form a plurality of annular corrugations in which the fibers are com pacted and distortedto alter the undesirable natural resonance characteristics of said diaphragm.

2. The method of making an acoustic dia phragm which comprises forming a seamless accreted fibrous diaphragm normally subject to undesirable natural resonance characteristics and having a border portion, a vibratile portion and a corrugation between said border and said vibratile portions, humidifying to increase the moisture content of the diaphragm, and reforming by pressing said accreted corrugation to form a plurality of annular corrugations in which the fibers are compacted and distorted to alter the undesirable natural resonance characteristics of said diaphragm.

3. The method of making an acoustic diaphragm which comprises forming a seamless accreted fibrous diaphragm normally subject to un- 'phragm which comprises forming a seamless accreted fibrous diaphragm normally subject to undesirable natural resonance characteristics and having a border portion, a vibratile portion and a corrugation between said border and said vibratile portions, lacquer treating said dia -g phragm, humidifying to increase the moisture content of the diaphragm, and reforming by pressing said corrugation to form a plurality of annular corrugations in which the fibers are com pacted and distorted to alter the undesirable natural resonance characteristics of said diaphragm.

5. The method of making an acoustic diaphragm which comprises forming a seamless accreted fibrous diaphragm normally subject to undesirable natural resonance characteristics and havinga border portion, a vibratile portion and a corrugation between said border and said vibra} tile portions, resin treating said diaphragm, drying said diaphragm, humidifying toincreasethe moisture content of the diaphragm, and reforming by pressing said corrugation to form a plurality of annular corrugations in which the fibers are compacted and distorted to alter the undesirable natural resonance characteristics of said diaphragm.

6. The method of making an acoustic diaphragm which comprises forming a seamless accreted fibrous diaphragm normally subject to undesirable natural resonance characteristics and having a border portion, a vibratile portion and a corrugation between said border and said vibratile portions, adjusting the moisture content of said corrugation and reforming by pressing said moist corrugation into aplurality of annular corrugations in which the fibers are compacted and distorted to alter the undesirable natural resonance characteristics of said diaphragm between embossing dies.

FRANK B. LENZ.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,927,902 Rose Sept. 26, 1933 1,989,015 McKellip Jan. 22, 1935 2,006,830 Hawley July 2, 1935 2,288,832 Pare July '7, 1942 2,411,066 Stevens Nov. 12, 1946 2,439,665 Marquis Apr. 13, 1948 

